The environmental toll of storing fossil fuels

As energy prices have swooned, inventories of all fossil fuels have grown to unusually high levels. Coal stockpiles have mounted, crude oil storage has filled and natural gas stocks remain unusually large for the spring season.

Most news coverage of these exceptionally large inventories has focused on their role in continuing to dampen prices for each of these fuels. Coal, oil and natural gas all sell for far less than their prices of a few years ago, even as oil prices have recovered slightly. Some of the stockpiling occurs as traders hope for higher prices in the future.

Beyond these market impacts of soaring inventories, far less has been written about the environmental toll of storing so much fossil fuel for so long. However, coal, oil and natural gas each pose distinct environmental problems in storage, even before their combustion releases emissions to the environment.

As I wrote in a previous column for The Hill, coal stockpiles have been growing everywhere, from the United States to China, as demand has slowed. Once coal is mined, it begins to react with air, releasing gases such as carbon dioxide and hydrocarbons. Coal stockpiles must be carefully managed to avert air pockets and heating that can enable spontaneous combustion to occur. Even with careful management, some of the heat content of the coal continues to be lost as it remains exposed to air.

As oil producers and traders await higher prices, companies have been quickly building new underground caverns and tank farms to expand storage capacity, especially in the Houston region. Oil storage requires careful management to minimize the release of hydrocarbons into the air. Recent research by HARC has measured elevated levels of benzene and other air toxics near pipelines and storage tanks near Houston. Benzene is a known carcinogen, and other evaporated hydrocarbons contribute to the formation of ground-level ozone smog and particulate matter.

The environmental damage from fossil fuel storage is most dramatically illustrated by the Aliso Canyon gas leak in California. Scientists estimate that the leak, also known as the Porter Ranch gas blowout, released about 100,000 tons of methane to the atmosphere. Methane is a climate warming gas many times more potent than carbon dioxide that also contributes to background ozone pollution. The leaks from Aliso Canyon occur not from fracking or drilling operations, but instead from the second-largest natural gas storage facility in the country.

While Aliso Canyon garnered the headlines, studies show that hundreds of other underground storage facilities leak natural gas (comprised mostly of methane) to the atmosphere. Though lesser in intensity, these leaks contribute to climate warming and mean that valuable fuel is being wasted without being burned for energy.

Together, the environmental impacts of storage highlight an often overlooked aspect of the life cycle of fossil fuels. Life cycle analysis quantifies the full environmental impacts of a fossil fuel from the time it is extracted to its end use. Many studies seek to quantify the environmental harm caused by mining for coal, drilling for oil or fracking for natural gas. Likewise, emission inventories are fairly reliable for estimating the amounts of greenhouse gases and air pollutants emitted from the end use combustion of fossil fuels.

However, the environmental impacts of the storage and transport steps in between fuel extraction and end use tend to be less well understood. Disperse leaks of pollution from oil and gas storage and coal oxidation are not directly measured, unlike exhaust passing through smokestack monitors or vehicle tailpipe testing. Thus, the environmental cost of storage is typically not factored in to energy market decisions. This may lead to excess amounts of storage, or insufficient efforts to mitigate oxidation or leaks and thereby save valuable fuel.

The Environmental Protection Agency (EPA) and industry have begun to take steps to mitigate emissions from oil and gas storage. More broadly, it is important to recognize that the full costs of fossil fuel storage extend beyond the direct expense of maintaining unsold assets and impact the environment as well.

Cohan is associate professor of civil and environmental engineering at Rice University.